This invention relates generally to cable television systems and specifically to a method of improving the operation of a cable system having one or more dedicated pay per view (PPV) channels.
U.S. Pat. No. 4,460,922 issued Jul. 17, 1984 in the names of J. Ensinger and M. Hendrickson, assigned to Zenith Electronics Corporation and incorporated herein by reference, describes generally the memory select system for the Z-TAC decoder manufactured by Zenith Electronics Corporation. That system includes in-band addressable subscriber stations, each with a unique address and authorization memory organized to provide a number of tiers or programming categories. The subscriber stations are supplied data on specific horizontal lines of the television signal vertical blanking interval (VBI). The patent describes a memory read and select technique that obtains the benefits of a system having a larger number of programming tiers without the detriment of increasing the bit length of the subscriber authorization codes. The authorization memory is divided into four so-called RAM groups, each comprising five tiers or programming categories, with one of the RAM groups being reserved for pay per view events.
A pay per view event differs from a premium service of the cable system in that the pay per view event is for a relatively short time. It generally consists of a single program, which may be periodically repeated. Premium services such as movie channels, sports channels and the like are generally provided on a continuing subscription basis. Pay per view programming, on the other hand, is provided on an individual "buy" basis. PPV events generally include special type movies which are offered a selected number of times during a month and "live" programs such as special sporting events. Such pay per view events are usually assigned to a specific one or more channels, each having its own encoder. The encoders accept subscriber address and authorization memory update and refresh information from the system controller and attempt to communicate with all subscriber stations by data addressed to the individual subscriber stations.
It is very desireable to be able to rapidly authorize subscriber stations to decode pay per view events and also to provide for recurring pay per view events on the same channel. Both the authorization and deauthorization processes must occur rapidly to effectively utilize the pay per view channel capability. In the Z-TAC system, the ability to rapidly authorize/deauthorize the subscriber stations is limited by the need to transmit an entire RAM group of the authorization memory to make any change as well as the need for the system controller to continually update and refresh subscriber station authorization memories as mentioned above. The system controller need not be involved for non-premium or so-called "basic" programming since such signals are not encoded. Indeed a subscriber station may not even have a decoder box if a cable-ready television receiver is installed.
Since communication between the cable head-end and the individual subscriber station is in-band, the subscriber station must be tuned to a data channel (i.e. one whose television signal carries data in the VBI) in,order to have its subscriber authorization memory changed or refreshed, both herein referred to as being updated. A "homing" channel is often provided for communications purposes, the homing channel being accessed automatically when the individual subscriber station decoder is turned off. The system controller, via the channel encoders, periodically and continually circulates authorization memory update information to the individual subscriber stations. However there are still situations in which a subscriber station does not tune to a data channel on a reasonably timely basis with the result that the subscriber station authorization memory may not be updated.
The in-band data format of the Z-TAC system limits the addressing rate to approximately 2700 subscriber stations per minute for a full four RAM group (20 program tags) authorization, or approximately 10,800 decoders per minute for a single RAM group authorization. While the addressing rate is more than adequate for premium channel service changes, new installation turn-ons and authorization memory refreshment, difficulty is encountered in rapidly authorizing and deauthorizing subscriber stations for pay per view events. This is especially true where the subscriber station may determine to "buy" a PPV program at the last minute.